1. Field of the Invention
This invention relates to storage tanks used for storing compressed gaseous fuels. In particular, the present invention is related to a mechanism for preventing the relative movement of tanks that are attached to vehicles using hoop brackets to safeguard against high pressure line breakages.
2. Description of the Prior Art
Cylindrical fuel tanks, such as compressed natural gas and compressed hydrogen gas tanks, are typically secured to the vehicle structure using hoop brackets. The high pressure tanks expand and contract during refueling and engine fuel consumption cycles, and are subject to ‘g’ forces induced by vehicle acceleration, deceleration, extended vibrations and collisions. Tanks that are mounted longitudinally (i.e., parallel to the vehicle axis) are especially prone to movement within the brackets either axially or rotationally, under repeated ‘g’ loads and expansion-contraction cycles.
For example, cylindrical fuel tanks which are mounted longitudinally on the roofs of buses or on the side of trucks may be prone to longitudinal sliding or hoop spinning within the brackets, causing breakage of high pressure gas lines affixed to the tanks. Any relative movement between a tank and brackets needs to be minimized to eliminate the risk of gas line breakage. This is a challenge especially for heavy tanks since the ‘g’ force is a product of the tank mass and the vehicle acceleration.
Typical bracket configuration includes an L-shaped bracket that is permanently bolted on the vehicle and a U-shaped strap that is attached to the L-shaped bracket and secures the tank in place (hereinafter “U-L joint”). A non-metallic gasket is typically placed between the tank and the brackets to prevent chafing damage of the tank shell and to allow some room for expansion. However, these conventional gaskets do not prevent lateral movement or rotation of the tank. In many cases, springs are deployed at the U-L joints to accommodate expansion-contraction cycles of the tank without damage to the bracket straps. However, the tanks can still move laterally.
The tank is prevented from moving longitudinally by frictional resistance between the non-metallic gasket and the tank. The frictional resistance depends on the coefficient of friction between the rubber gasket and the composite shell, and is proportional to the pressure applied by the bracket on the tank surface. Unfortunately, the pressure applied by the bracket on the tank decays with time, due to relaxation of the bracket material and loosening of the U-L joint under tank expansion-contraction cycles and repeated ‘g’ forces. As a result of the reduced frictional resistance between the brackets and the tank, the tank may slide longitudinally and or rotate, creating the safety hazard of gas line breakage.
Therefore, a cost-effective method is required for preventing the relative movement of tanks that are attached to vehicles using hoop brackets to safeguard against high pressure line breakages.